gma ddi: Don't try to disable non-existent DDI D

Didn't hurt on Haswell-/Broadwell-U, but did lock up Broxton.

Change-Id: I6a47d0fba8cb6e59d8ace1ab64eed6182769a37b
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/18420
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/haswell_shared/hw-gfx-gma-port_detect.adb b/common/haswell_shared/hw-gfx-gma-port_detect.adb
index bf9fba5..b8ba37d 100644
--- a/common/haswell_shared/hw-gfx-gma-port_detect.adb
+++ b/common/haswell_shared/hw-gfx-gma-port_detect.adb
@@ -59,9 +59,6 @@
       Internal_Detected,
       DDI_Detected : Boolean;
 
-      Last_Digital_Port : constant Digital_Port :=
-        (if Config.Has_DDI_D then DIGI_D else DIGI_C);
-
       subtype Ext_Digital_Port is
          Digital_Port range DIGI_B .. DIGI_D;
       type Digital_Port_To_GMA_Port is array (Ext_Digital_Port) of Port_Type;
@@ -116,7 +113,7 @@
       Config.Valid_Port (Internal) := Internal_Detected;
 
       -- DDI_[BCD]
-      for Port in Ext_Digital_Port range DIGI_B .. Last_Digital_Port loop
+      for Port in Ext_Digital_Port range DIGI_B .. Config.Last_Digital_Port loop
          Registers.Is_Set_Mask
            (Register => Registers.SFUSE_STRAP,
             Mask     => DDI_PORT_DETECTED (Port),